The present invention generally relates to information services provided on a broadcast basis within a wireless communication network, such as a cellular communication network, and particularly relates to controlling the number of service cells used to support such services for one or more mobile stations.
One of the most striking points regarding the evolution of Public Land Mobile Networks (PLMNs), such as cellular voice and data networks, is the increasing variety and sophistication of the available services. One of the newer services associated with the expanding data capabilities of current and planned wireless networks is broadcast/multicast service. With that service type, an information stream, such as a streaming news report, is “broadcast” on a commonly available channel within one or more cells of the network such that a plurality of mobile stations may simultaneously receive the information stream by “tuning” to the broadcast/multicast channel.
Because the intent of such services is to provide essentially “blanket” coverage at least within a defined service area, such broadcast channels are resource intensive in terms of the transmit power allocated to them. In this sense, a broadcast channel signal is similar to a paging channel signal in that it is transmitted with a relatively high transmit power to ensure adequate reception throughout the coverage area of a given radio base station. However, the data rate of the average broadcast channel signal is much higher than that of the average paging channel, e.g., 64 Kbps versus 4.8 Kbps, so the transmit power required to achieve similar coverage for the broadcast channel is potentially much higher than that used for standard paging channels.
Several practical considerations thus arise when providing such broadcast channels within a cellular communication network. First, because such channels are so resource intensive, the capacity of the network is unduly compromised and resources that might otherwise be used to support other services for other users are wasted unless the region(s) in which a given broadcast channel is activated is reasonably restricted to the areas in which mobile stations are actually tuned to the broadcast channel. That is, the number of network transmitters used to transmit the broadcast channel signal would ideally be restricted to just the cell or cells where the mobile stations tuned to the service are located.
However, the idealized service area restrictions may not yield acceptable service from the perspective of mobile station users interested in receiving the broadcast service. For example, assume that a mobile station within a network service cell registers for an information stream, and the network activates a broadcast channel signal for that stream in response. If the broadcast channel signal is transmitted only within the mobile station's current cell, then service disruptions will result if the mobile station moves out of the current cell's coverage area into the coverage area(s) of one or more neighboring cells.
Thus, to minimize such disruptions, the network operator may activate the service not only in the current cell but also within a range of neighboring cells. Establishing the range of neighboring cells that are activated is, however, a key challenge in balancing the desire to avoid (or at least minimize) service interruptions for a moving mobile station with the desire to efficiently use network resources. In current approaches, the range of neighboring cells in which the service is activated includes those within a geographic range that is set according to a periodic service registration timer in the mobile stations. Using a shorter periodic registration timer enables the use of smaller geographic ranges but increase the signaling overhead in the network.